1. Field of the Invention
This invention relates to a material handling car and track assembly and is directed more particularly to a track configuration and a car wheel assembly for cooperation with the track to keep the car on the track.
2. Description of the Prior Art
It is known generally in car and track systems to utilize opposed U-shaped channel members as track rails and to provide both horizontal and vertical wheels on the car. In such arrangements, the vertical wheels usually serve as main travel wheels and the horizontal wheels ride along the inboard vertical walls of the channel members to keep the travel wheels centered on the rails.
In U.S. Pat. No. 3,265,190, issued Aug. 9, 1966, to Walter G. Boehm, there is disclosed a car adapted to travel on opposed U-shaped channel members. The car is provided with two vertical travel wheels on each side of the car which are disposed within a track channel member. Between each pair of travel wheels on a side is a horizontal roller which engages an inboard upper edge of the channel member.
U.S. Pat. No. 3,231,066, issued Jan. 25, 1966 to Walter G. Harrison, et al., discloses a car adapted to move on parallel rails. The car is provided with four vertical wheels for riding on horizontal rail portions, and a single horizontal wheel, disposed centrally of the car, for contacting vertical rail means disposed between the parallel rails.
In U.S. Pat. No. 4,919,054, issued Apr. 24, 1990, to Yukito Matsuo, there is disclosed a car adapted to run on opposed U-shaped rails. In one embodiment, each car is provided with four pairs of vertical wheels. In each pair of vertical wheels, there is a lower wheel for engaging a bottom plate portion of the rail and an upper wheel for engaging a top plate portion of the rail. Associated with each pair of vertical wheels, but spaced therefrom along the length of the car is a horizontal wheel adapted to engage a vertical plate portion of the rail.
In Matsuo, the car is propelled by a linear induction motor, disposed well beneath the level of the rails, acting upon a vane depending from the car and adapted to pass through a slot in the motor, which imparts thrust to the vane, and thereby the car. Inasmuch as the vane is disposed well below the wheels of the car, each thrust forward on the vane imparts a turning moment on the car, a stress which, experienced thousands of times, causes undue wear on the car and the rails.